Vehicle trajectory control system and method

ABSTRACT

A method for controlling a powertrain of a vehicle is described. The method determines a desired vehicle condition based on three driver actuated elements. In a preferred embodiment the first element can be pedal position, the second element can be a brake actuator or, more specifically, brake actuation duration, and the third element can be a gear selection lever. Further, the desired vehicle condition can be desired powertrain output, vehicle acceleration, or various other parameters.

FIELD OF THE INVENTION

The present invention relates to automotive vehicles, and moreparticularly to powertrain control of automotive vehicles.

BACKGROUND OF THE INVENTION

Various methods can be used in controlling a vehicle powertrain inresponse to driver requests. In one approach, from an accelerator pedalactuation or brake pedal actuation, a controller determines theacceleration of the vehicle (of positive and/or negative nature, desiredby the driver. This acceleration is then used in influencing the wheeldrive of the motor vehicle. In lieu of the desired acceleration of themotor vehicle, wheel torque can be used. Such a system is described inU.S. Pat. No. 5,351,776.

The inventors herein have recognized several disadvantages with theabove approach. In particular, assuming such an approach is utilizedwith a brake system in which the brake signal is simply on or off, thedriver would have very low resolution in selecting the desired amountsof deceleration or negative wheel torque. Further still, the driver maydesire a different amount of deceleration or negative wheel torque aftera short brake actuation versus a long brake actuation. The aboveapproach would not take such driver desires into account. Yet anotherdisadvantage with prior approaches recognized by the inventors is thatthe driver may desire a different mapping between pedal (or brake)actuation and desired acceleration or wheel torque. In particular, ifthe transmission gear selector is in “DRIVE” versus “LOW” (typically,the selections are PRNDL: park, reverse, drive, neutral, and low), notonly may different transmission gears be selected, but also differentaccelerations or wheel torques may be desired.

SUMMARY OF THE INVENTION

Disadvantages of prior approaches are overcome by a method forcontrolling a powertrain of a vehicle. The method comprises detectingoperation of a first driver actuated element, detecting operation of asecond driver actuated element, detecting operation of a third driveractuated element, and determining a desired vehicle condition based onsaid detected first, second, and third driver actuated element. Thefirst element can be pedal position. The second element can be a brakeactuator or, more specifically, brake actuation duration. The thirdelement can be a gear selection lever.

By including brake duration, it is possible to provide the driverimproved resolution depending on how long the brake actuator isdepressed. Further, it is possible to provide more tailored drive feelby providing different vehicle operation depending on the position ofthe gear selection lever.

Advantages of the present invention can include improved vehicleperformance and operation.

It is important to note that the first, second, and third elements canbe other elements than those noted above. For example, they can be acruise control actuator, a turn signal actuator, or a clutch actuator.Further, the determined vehicle condition can be a desired vehicleacceleration, a desired powertrain output torque, or a desiredtransmission gear ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are block diagrams of an embodiment wherein the invention isused to advantage;

FIGS. 3-18 are high-level flow charts of various operations performed bya portion of the embodiment shown in FIG. 1;

FIG. 19 is a graph illustrating operation according to the presentinvention; and

FIGS. 20-23 are block diagrams of torque converters that can be usedaccording to the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, further describedherein with particular reference to FIG. 2, is shown coupled to torqueconverter 11 via crankshaft 13. Torque converter 11 is also coupled totransmission 15 via transmission input shaft 17. Torque converter 11 hasa bypass clutch (described in FIGS. 20-23), which can be engaged,disengaged, or partially engaged. When the clutch is either disengagedor partially engaged, the torque converter is said to be in an unlockedstate. Transmission 15 comprises an electronically controlledtransmission with a plurality of selectable discrete gear ratios.Transmission 15 also comprises various other gears such as, for example,a final drive ratio (not shown). Transmission 15 is also coupled to tire19 via axle 21. Tire 19 interfaces the vehicle (not shown) to the road23. In a preferred embodiment, transmission 15 has the following driverselectable optionsa: park (P), reverse (R), neutral (N), driver (D), andlow (L). The driver selects these positions via a transmission lever. Inthis preferred embodiment, the lever is known as the PRNDL lever,corresponding to the different options. In particular, in park orneutral, transmission 15 does not transmit torque from the transmissioninput to the output. In drive, a transmission controller can controltransmission to select any available forward gear ratios. In reverse, asingle reverse gear is selected. In low, only a lower set of forwardgear ratios can be selected by the electronic controller. Those skilledin the art will recognize, in view of this disclosure, various othertypes of transmission levers with different sets of options that can beused with the present invention. For example, there can be low 1 and low2 options. Also, the transmission lever may be located on a steeringcolumn or between driver and passenger seats.

Internal combustion engine 10 comprises a plurality of cylinders, onecylinder of which is shown in FIG. 2. Electronic engine controller 12controls Engine 10. Engine 10 includes combustion chamber 30 andcylinder walls 32 with piston 36 positioned therein and connected tocrankshaft 13. Combustion chamber 30 communicates with intake manifold44 and exhaust manifold 48 via respective intake valve 52 and exhaustvalve 54. Exhaust gas oxygen sensor 16 is coupled to exhaust manifold 48of engine 10 upstream of catalytic converter 20.

Intake manifold 44 communicates with throttle body 64 via throttle plate66. Throttle plate 66 is controlled by electric motor 67, which receivesa signal from ETC driver 69. ETC driver 69 receives control signal (DC)from controller 12. Intake manifold 44 is also shown having fuelinjector 68 coupled thereto for delivering fuel in proportion to thepulse width of signal (fpw) from controller 12. Fuel is delivered tofuel injector 68 by a conventional fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown).

Engine 10 further includes conventional distributorless ignition system88 to provide ignition spark to combustion chamber 30 via spark plug 92in response to controller 12. In the embodiment described herein,controller 12 is a conventional microcomputer including: microprocessorunit 102, input/output ports 104, electronic memory chip 106, which isan electronically programmable memory in this particular example, randomaccess memory 108, and a conventional data bus.

Controller 12 receives various signals from sensors coupled to engine10, in addition to those signals previously discussed, including:measurements of inducted mass air flow (MAF) from mass air flow sensor110 coupled to throttle body 64; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling jacket 114; a measurement ofthrottle position (TP) from throttle position sensor 117 coupled tothrottle plate 66; a measurement of turbine speed (Wt) from turbinespeed sensor 119, where turbine speed measures the speed of shaft 17;and a profile ignition pickup signal (PIP) from Hall effect sensor 118coupled to crankshaft 13 indicating and engine speed (N).

Continuing with FIG. 2, accelerator pedal 130 is shown communicatingwith the driver's foot 132. Accelerator pedal position (PP) is measuredby pedal position sensor 134 and sent to controller 12.

In an alternative embodiment, where an electronically controlledthrottle is not used, an air bypass valve (not shown) can be installedto allow a controlled amount of air to bypass throttle plate 62. In thisalternative embodiment, the air bypass valve (not shown) receives acontrol signal (not shown) from controller 12.

FIGS. 2-17 describe various routines carried out by controller 12. Theroutines are preferably carried out in the order in which they arenumbered, unless called by an earlier routine. However, those skilled inthe art will clearly recognize in view of this disclosure, that variousaspects of the Figures and various calculations can be rearranged innumerous orders without departing from the scope of the invention.

Referring now to FIG. 3, a routine is described for determining thedesired engine torque for use in the engine control system. First, instep 310, a driver requested wheel torque, or output shaft torque, iscalculated based on pedal position and vehicle speed. In particular, thedriver requested torque (tqo_arb_req) is calculated as a two-dimensionallook-up table as a function of pedal position (PP) and vehicle speed(vspd). Next, in step 312, a limit torque (tqo—arb_lim) is determined.This limit output torque can be provided from various sources, forexample, from vehicle speed limiting, traction control limiting, or froma vehicle stability control system. When the transmission controllerprovides the limit output torque, this torque can represent maximumallowable torque that can be transmitted through the transmission. Next,in step 314, the routine calculates a driver engine torque request formanual transmissions and automatic transmissions in neutral, park, orsome driver selected gears (tqe_dd_req). Note that the tqe_dd_req is aseparate parameter then the one calculated in step 310, when tqe_arb_reqis calculated for automatic transmissions when the transmission is in agear other then neutral or park. Next, in step 316, the routine convertsdriver wheel torque request and limit torque to engine torque requestusing overall ratio G1 (which includes gear ratio, torque convertertorque ratio, transmission efficiency), and torque loss parameter LOSS,which preferably represent friction. Next, in step 318, the routineselects the maximum of the tqe_dd_req and tqe_arb_req. In this way, theroutine arbitrates the proper engine torque request taking into accountwhether an automatic transmission or manual transmission is present inthe vehicle. Further, the routine provides for automatic transmissionsoperated in a mode, such as neutral or park, when the engine is notcoupled to drive the wheels.

Referring now to FIGS. 4A and 4B, a routine is described whichcalculates a desired vehicle speed trajectory and which filters andlimits the torque request to provide various advantages as describedlater herein. First, in step 410, a routine calculates the vehicle speedtrajectory based on position of the gear selector (PRNDL), vehicle speed(vspd), and the brake pedal (BOO).

In particular, the routine calculates the maximum vehicle speed during atip-out (tq_vs_des_mx). As described later herein, this vehicle speedtrajectory is used to determine whether negative engine torque isrequired. Those skilled in the art will recognize, in view of thisdisclosure, that various other parameters can be used to provide adesired vehicle trajectory such as acceleration or deceleration.Alternatively, timers could be used to determine if a selected operatingconditions is achieved by a set time.

Continuing with FIG. 4A, the routine proceeds to step 412 where adetermination is made as to whether the pedal position is at closedpedal. This is done, for example, by checking the flag APP. Flag APP isset to minus 1 when, for example, PP is less than a predetermined valueindicated the driver has released their foot, or when the pedal angle isalmost completely released. In other words, in this implementation, theroutine determines whether the driver has positioned the pedal in themost released position, known to those skilled in the art as closedpedal. When the answer to step 412 is yes, the routine continues to step414 where the desired engine torque is rate limited. Then, in step 416,the requested torque is limited to a minimum of zero. Parametertqe_daspot represents the minimum clip on requested torque. The equationin step 414 provides a second order function, which is preferable fordrive feel. Those skilled in the art will recognize, in view of thisdisclosure, that various filtering methods could be used such as a firstorder low pass filter or a rate-limiting filter.

When the answer to step 412 is no, the routine continues to step 430 inFIG. 4b. In other words, when the driver is not in a closed pedalcondition, which means in a part or wide-open pedal position, theroutine calculates the rate limited torque as a portion of thedifference between the current driver demand and the minimum allowedtorque (tqe_desmaf) determined in part from the misfire line asdescribed later herein. Next, in step 432, a determination is made as towhether temporary filtered torque (tqe_daspot_tmp) is greater thenfiltered desired torque (tqe_daspot). Depending on the outcome of step432, a temporary multiplier is set. In particular, this temporarymultiplier adjusts a filtering time constant for filtering enginetorque. The filter constant is set to different levels depending onwhether desired engine torque is increasing or decreasing. Step 434 setsthe multiplier for an increase in torque. Step 436, sets the multiplierfor a decrease in desired torque. Steps 438, 440, and 432 describe thedetails of how the desired engine torque is filtered. The time constant(tcdasf) is calculated in step 438. Then, the filter constant iscalculated as a function of the sample time and the parameter (tcdasf).Finally, in step 442, the filtered desired engine torque is calculatedwith a low pass filter (LPF). Those skilled in the art will recognize,in view of this disclosure, that various types of filters can be usedrather than a low pass filter such as rate limiting filters or lead lagfilters.

Referring now to FIG. 5, a routine is described which continues thedetermination of desired engine torque from FIGS. 4a and 4 b. First, instep 510, a determination is made as to whether the requested enginetorque from step 318 (tqe_arb_req) is less than the filtered desiredengine torque (tqe_daspot). When the answer to step 510 is no, theroutine continues to step 512 when a flag (tq_dd_limit) is set to zero.Otherwise, in step 514, the desired engine torque is set equal to thefiltered engine torque. Next, in step 516, the flag (tq_dd_limit) is setto minus one. In this way, regardless of pedal angle, the filteredengine torque is applied as a minimum clip on the driver requestedengine torque.

Referring now to FIG. 6, a routine is described for determining whetherthe driver is in a closed pedal position, wherein closed pedal engineand vehicle controls are executed. First, in step 610, a flag isinitialized (tq_dd_mode=zero). This step is only executed at key-on orat part throttle conditions. This flag is used in the closed pedal statemachine to determine which state is executed. As described later herein,the state machine operates from case zero up to case 6. The flagtq_dd_mode determines which case is executed.

In step 612, a determination is made as to whether a tip out conditionis present via flag APP. In other words, a determination is made as towhether the measured accelerator pedal position is less than apredetermined value indicating the pedal is in the fully releasedposition. Those skilled in the art will recognize, in view of thisdisclosure, various ways for determining whether a closed pedal, ortip-out condition, is present. For example, vehicle speed oracceleration, engine torque determination, or various other methodscould be used.

Continuing with FIG. 6, when the answer to step 612 is no, the routinedetermines that the condition is part throttle or wide-open throttle andexecutes the routine described in FIG. 14. When the answer to step 612is yes, the routine continues to step 614, where a determination is madeas to whether the flag trg_n_t_flg is TRUE. In other words, the routinedetermines whether the engine is in the feedback engine speed controlmode. There are various places where the engine is in the closed loopengine speed control mode such as, for example, during a manual pull inwhen the transmission requests an engine speed to match the future gearratio; when the current gear does not provide engine braking asdescribed later herein; or during a neutral to drive engagement. Forexample, during a neutral to drive engagement or a manual pull in (wherethe driver changes the selected PRNDL position), the transmission candelay the actual gear change until the engine speed is brought to adesired engine speed. In these examples, the desired engine speed can beselected to equal the synchronous speed in the future gear ratio. Inthis way, transmission wear is minimized since the gear ratio can beperformed with the engine speed close to the engine speed that will beachieved after the gear change is completed. In another example relatingto when the current gear does not provide engine braking, the desiredengine torque is calculated to that the transmission input speed is at,or slightly below, the measured transmission output speed times thecurrent gear ratio of the transmission. In this way, there is no delay,and transmission gear clunk is minimized, when positive powertrainoutput torque is again applied. Stated another way, the desired enginespeed can be set to (or slightly below) the synchronous speed, where thesynchronous speed is based on the transmission state (selected gearratio) and the transmission output speed. Such a method can be used whenthe current selected transmission ratio does not provide engine braking.In this speed control, as described later herein, a desired torque isselected to cause the speed error to approach zero. As described, torquecontrol can be accomplished via various engine operating parameters suchas air/fuel, ignition timing, throttle angle, or any other availabletorque actuator.

When the answer to step 614 is no, the state machine is called and thecase is executed which corresponds to the current condition of flagtq_dd_mode in step 616. Otherwise, the routine continues to 618 wherethe flag is set to 7. Then, the desired engine torque is calculatedusing a PI controller known to those skilled in the art as aproportional integral controller based on an engine speed errorcalculated from the difference between the desired engine speed (Ndesminus N).

Referring now to FIG. 7, case zero of the state machine is described.Case zero is generally called to initialize the state machine. First, instep 710, a determination is made as to whether the requested arbitratedtorque is greater than a small positive calibratable engine torque(TQE_SML_POS). When the answer to step 710 is yes, the state machineflag is set to 1 in step 712. Otherwise, the state machine flag is setto 2 in step 714.

Referring now to FIG. 8, case 1 of the state machine is described. Asdescribed above, case 1 is called when flag tqe_dd_mode is equal to 1 instep 616. In step 810, a determination is made as to whether the desiredengine torque is less than or equal to the calibratable small positivetorque (TQE_SML_POS). When the answer to step 810 is yes, the flagtqe_dd_mode is set to 2 in step 812.

Referring now to FIG. 9, case 2 of the state machine is described.First, in step 910, a determination is made as to whether the currentactual vehicle speed (vspd) is greater than the sum of the maximumallowed speed during the tip out condition (tq_vs_des_mx) plus theallowed over-speed error (vsdeltogoneg). The allowed over-speed errorcan be a single value or can vary with engine operating parameters. Forexample, depending on selected gear ratio and vehicle speed, it may bedesirable to have different thresholds of allowed over-speed error. Suchan approach may reduce excessive shifting, also known as shift busyness.When the answer to step 910 is yes, the state machine flag (tq₁₃ dd₁₃mode) is set equal to 3. In other words, when the actual vehicle speedis greater than the desired vehicle speed trajectory, plus the tolerancevalue, the state machine then executes in the next call of step 616,case 3, which executes a torque crossing from positive powertrain outputtorque to negative powertrain output torque, as described later hereinwith particular reference to FIG. 10. As described above, those skilledin the art will recognize, in view of this disclosure, that variousother vehicle parameters can be used to calculate the desired vehiclespeed trajectory and determine if the actual vehicle trajectory is belowthe desired vehicle trajectory.

When the answer to step 910 is no, the routine continues to step 914,where a determination is made as to whether the torque converter islocked. When the answer to step 914 is no, the routine continues to step918. In step 918, a positive output torque is provided including closedloop control using torque converter input and/or output speeds. In thisparticular case, a desired engine speed is calculated to be greater thanthe measured torque converter output or turbine speed. This desiredengine speed is used with a closed loop proportional integral (PI)controller to calculate a desired engine torque request. In this way,feedback control is used to maintain a positive output torque. Theparameter (TQ₁₃ N₁₃ SML₁₃ POS) is a calibratable parameter to provide asafety factor that minimizes inadvertent zero torque crossings due toexternal factors such as road grade. In other words, the controller'sobjective is to maintain engine speed greater than torque converteroutput speed. Those skilled in the art will recognize, in view of thisdisclosure, that additional feedback can be included, wherein suchfeedback could be from sensors such as a torque sensor, mass airflowsensor, or other sensors used in torque or speed control.

Alternatively, when the torque converter is locked, the desiredarbitrated engine torque is set to the small positive torque (TQE₁₃SML₁₃ POS). In this case, the powertrain is controlled to provide apositive output torque and minimize inadvertent transitions through thezero torque point. Since the torque converter is locked, an open loopcontrol approach is used where feedback from torque converter input andoutput speeds based on a torque converter model are not used. However,other feedback variables can be used in providing the torque controlsuch as, for example, a torque sensor, or a mass airflow sensor. Inparticular, torque transmitted by the powertrain (engine output torque,transmission torque, or wheel torque) can be estimated based onoperating conditions such as, for example, mass airflow, manifoldpressure, engine speed, ignition timing, coolant temperature, and otheroperating conditions.

By providing such control of maintaining positive powertrain output,inadvertent zero torque crossings will be minimized and improved vehicledrive feel can be achieved.

Referring now to FIG. 10, case 3 of the state machine is described.First, in step 1010, a determination is made as to whether thearbitrated requested engine torque is less than a small negative outputtorque (TQE₁₃ SML₁₃ NEG), or the small negative torque is apredetermined calibratable parameter. When the answer to step 1010 isyes, then the state machine flag tq₁₃ dd₁₃ mode is set to 4 in step1012. Otherwise, in step 1014, the requested engine torque is slowlydecremented to gently pass through the zero torque point. In this way,once the negative engine torque is provided, the routine will transitionto case 4, and until the negative engine torque is provided, the routinewill provide a gradual decrease from the small positive torque to thesmall negative torque so that clunk occurring at the zero torque pointis minimized.

Referring now to FIG. 11, case 4 of the state machine is described.First, in step 1110, a determination is made as to whether a largenegative engine torque is required by determining if flag (rdy₁₃ very₁₃neg) is TRUE. Typically, the flag is set TRUE by the transmissioncontrol system to indicate that the torque converter is locked. In otherwords, various types of torque converters cannot be locked when thepowertrain is transmitting large negative torques. Thus, the presentinvention can prevent large negative engine torques until the torqueconverter is locked, if such a torque converter is used. When the answerto step 1110 is yes, the state machine flag (tq₁₃ dd₁₃ mode) is set to 5in step 1112. Otherwise, a determination is made as to whether thetorque converter is locked in step 1114. When the torque converter islocked, the required engine torque is set to a small negative value(TQE₁₃ SML₁₃ NEG), which is predetermined calibratable value. In step1116, the negative engine torque is provided in an open loop modewithout feedback from the torque converter input and output speeds.Otherwise, in step 1118, closed loop engine speed control is providedwhere the desired engine speed is calculated to be slightly less thanthe torque converter output speed. Thus, in step 1118, feedback from thetorque converter input speed and output speed is utilized to minimizeinadvertent zero torque transitions.

Referring now to FIG. 12, case 5 of the state machine is described. Instep 1210, a determination is made as to whether the current vehiclespeed (vspd) is greater than the maximum allowed vehicle speedtrajectory value (tq₁₃ vs₁₃ des₁₃ mx). When the answer to step 1210 isyes, the routine continues to step 1212 where state machine flag (tq₁₃dd₁₃ mode) is set to 6.

Referring now to FIG. 13, case 6 of the state machine is described.First, in step 1310, a determination is made as to whether measuredvehicle speed (vspd) is less than equal to the desired vehicle speedtrajectory plus a predetermined calibratable value (TQ₁₃ VS₁₃ DESHYS).When the answer to step 1310 is yes, the routine continues to step 1312where the state machine flag (tq₁₃ dd₁₃ mode) is set to 5. Otherwise,the routine continues to step 1314 where feedback control vehicle speedis executed to provide the desired deceleration rate and the desiredvehicle speed trajectory. In particular, a PI controller known to thoseskilled in the art as a proportional integral controller is used withthe desired maximum allowed vehicle speed and the actual speed tocalculate the desired engine torque. In this way, engine torque controlis provided to give a desired vehicle trajectory.

If the state machine is called and none of the cases are executed, thedefault case is case zero.

Referring now to FIGS. 14a and 14 b, a routine is described for ratelimiting desired engine torque when desired powertrain output isincreasing. In step 1410, a determination is made as to whether thedesired engine torque is greater than the current requested enginetorque. In other words, a determination is made as to whether thedesired engine output is increasing. When the answer to step 1410 isyes, a determination is made in step 1412 as to whether the currentengine requested torque is less than or equal to a small negative torquevalue (TQE₁₃ SML₁₃ NEG). When the answer to step 1412 is yes, theroutine continues to step 1414, where the desired engine torque is ratelimited at a first rate determined by function G1. In other words, whenthe desired engine torque is increasing but negative and less than apredetermined negative engine torque, the desired engine torqueincreasing rate is limited to a first predetermined rate, wherein thepredetermined rate is dependent on the transmission gear selected or thecurrent transmission gear ratio. When the answer to step 1412 is no, theroutine continues to step 1416, where a determination is made as towhether the current requested engine torque is less than a smallpositive calibratable value (TQE₁₃ SML₁₃ POS). In other words, adetermination is made as to whether the current requested engine torqueis near the zero torque point. When the answer to step 1416 is yes, theroutine continues to step 1418, where the desired engine torqueincreasing rate is limited based on function G2. Generally, the maximumallowed rate of increase of engine torque in this region (near the zerotorque point) is less than the allowed increasing engine torque rateoutside of this region. When the answer to step 1416 is no, the routinecontinues to step 1420, where engine torque increasing rate is limitedto a third predetermined rate based on function G3. Stated another way,that allowed increasing rate of torque is greater when for the regionsaway from the zero torque region.

In this way, the present invention provides for three different engineincreasing torque rate limits depending on the current engine torquevalue. In particular, when desired engine torque is increasing and alarge negative value, it is rate limited at a first value. When desiredengine torque is increasing near zero torque point, it is rate limitedat a second, generally lower rate. Finally, when desired engine torqueis increasing and a large positive value, it is rate limited at a thirdrate. In addition, any combination of the above three rate limits may beused. For example, engine torque may be limited only when transitioningthrough the zero torque point, or engine torque may be limited only whentransitioning through the zero torque point and when increasing abovezero torque, engine torque may be limited only when transitioningthrough the zero torque point and when increasing below zero torque.Additionally, rate limits can be set as a function of the current, orselected, gear ratio, since different rate limits may be appropriatedepending on the actual transmission gear, or based on the selected gearas indicated by the transmission lever (PRNDL). Also, as describedherein, rate limiting may be used for decreasing torque when passingthrough the zero torque region.

From step 1414, the routine continues to step 1422, where adetermination is made as to whether the current requested engine torqueis greater than the rate limited engine torque. When the answer to thisis yes, the desired engine torque is set equal to the rate limitedtorque and a rate limiting flag (tq₁₃ dd₁₃ limit) is set to 1.Otherwise, the flag is set to zero in steps 1424 and 1426. From step1418, the routine continues to step 1428, where the same determinationas step 1422 is made. When the answer to step 1428 is yes, the desiredengine torque is set equal to the rate limited engine torque and theflag (tq₁₃ dd₁₃ limit) is set to 2 is step 1430. Otherwise, in step1432, the flat is set to zero. From step 1420, the same determination asin steps 1422 and 1428 is made in step 1434. When the answer to step1434 is yes, the desired engine torque is set to equal to the ratelimited value and the flag is set to 3 in step 1436. Otherwise, in step1438, the flag is set to zero.

Referring now to FIG. 15, a routine is described for arbitrating betweenvarious torque limits and the desired rate limited torque request. Insteps 1510, 1512, and 1514, the rate limited desired engine torquerequest is compared with the various maximum torque limits that preventengine speed from becoming greater than a predetermined value (tqe₁₃rpm₁₃ lim) and which prevent torque being requested which is greaterthan the maximum allowable torque transmitted through the transmission(tqe_max_tran).

Referring now to FIGS. 16a and 16 b, a routine is described forcontrolling engine torque while maintaining a minimum airflowrequirement. In particular, the following routine provides a method toprevent engine stalls when there is a rapid decrease in required enginetorque.

First, in step 1610, anti-stall torque line (tqe₁₃ antistal) iscalculated, which is the minimum indicated torque allowed as a functionof engine speed minus desired idle speed and the torque control source(tq₁₃ source). Parameter tq₁₃ source is the dominant determinant of thetorque reduction, i.e., whether vehicle speed limiting, tractioncontrol, or shift modulation are limiting torque. Thus, since dependingon which limit is controlling, a more aggressive position can be takenon how close to the anti-stall torque line the engine is operated.

Next, in step 1612, the desired engine torque arbitrated request iscompared with the anti-stall torque line and the maximum of theseparameters is selected. Next, in step 1614, the equivalent indicatedengine torque at the minimum allowed airflow and mapped spark valuebelow which engine misfires occur is called. This value is determined asa function of engine speed. Next, in steps 1616 and 1618, the transformof engine required idle airflow is determined. First, a multiplier(idle₁₃ am₁₃ mul) is determined as a function of the difference betweenthe desired engine speed and the actual engine speed, and the differencebetween the current vehicle speed and a minimum vehicle speed at whichidle speed control is engaged (minmph). FIG. 16c illustrates an exampletable showing that as the difference in vehicle speed or difference inengine speed becomes smaller, the minimum allowed airflow is graduallyadjusted to become equal to the airflow required at idle conditions.

Then, in step 1618, the multiplier is used to adjust the requiredairflow to maintain a desired engine speed at idle conditions. Then, instep 1619, this adjusted airflow is converted to a load value bydividing by the number of cylinders (numcyl₁₃ 0), engine speed (N), andthe amount of air that fills the cylinder at standard temperature andpressure (sarchg). Next, in step 1620, this desired load is converted toa torque using the conversion factor (TQ₁₃ 2 ₁₃ LOAD). Finally, in step1622, the maximum of the torque due to minimum airflow from misfires andthe torque due to the minimum air to guarantee engine idle speed controlis selected.

Continuing with FIG. 16b, this selected torque is then converted to anairflow request in step 1624. Next, in step 1626, this selected torquerequest is converted from an indicated torque to an engine brake torquerequest by subtracting the torque losses (tqe₁₃ los). Finally, in step1634, the engine torque request for scheduling the required airflow forthe electronic throttle control system is selected at the maximum of theparameter determined in step 1626 and the current engine brake request.

In this way, according to the present invention, when engine and vehicleoperating conditions are away from an idle speed control range, engineairflow can be reduced below the required engine airflow for maintainingidle speed. In this way, it is possible to provide large negative enginebrake torques to maintain vehicle trajectory under a variety of vehicleoperating conditions. However, as the vehicle conditions approach anengine idle speed region, airflow is increased to a required engine idlespeed control level. In this way, even despite the engine airflow delaysdue to manifold volume, it is possible to maintain robust idle speedcontrol as well as provide large negative engine braking ability.

Referring now to FIG. 17, a routine is described for calculating adesired vehicle trajectory, which is called in step 410 of FIG. 4a.First, a determination is made as to whether flag (APP) is less thanzero. In other words, a determination is made in step 1710 as to whethera closed pedal (tip-out condition) is present. When the answer to step17 is yes, the desired closed pedal acceleration (ct₁₃ accl₁₃ des) iscalculated as a function of the current vehicle speed and the gearselected position (PRNDL). Next, in step 1714, a determination is madeas to whether the brake pedal is released. When the answer to step 1714is yes, a determination is made as to whether the brake pedal engagementduration (boo₁₃ duration) is greater than zero in step 1716 indicatingthe first pass through the routine since the brake was depressed. Whenthe answer to step 1716 is yes, the vehicle speed release value (vs₁₃on₁₃ release) is set equal to the current vehicle speed and the lastbrake engagement duration is set equal to the current brake engagementduration value in step 1718. Next, in step 1720, a determination is madeas to whether the first brake engagement duration (boo₁₃ 1st) is greaterthan a predetermined duration (tq₁₃ boo₁₃ long) and the flag (tq₁₃ frz₁₃vsboo) is true. Flag (tq₁₃ frz₁₃ vsboo) is a selection flag that allowsusing brake duration in determing the maximum allowed vehicle speedtrajectory. Parameter (tq boo long) represents the braking durationafter which the maximum allowed vehicle speed trajectory will be heldconstant. In other words, if the driver simply taps the brake, themaximum allowed vehicle speed will continue to ramp toward zero afterthe brake is released. However, if the driver holds the brake pedal forlonger than a predetermined value, the maximum allowed vehicle speed isheld to the vehicle speed when the brake was released. This can give thedriver the ability to set a desired speed using the brake on a longdownhill grade.

Continuing with FIG. 17, when the answer to step 1720 is yes, themaximum allowed vehicle speed is set to parameter vs_on_release in step1722. When the answer to step 1720 is no, the maximum allowed vehiclespeed is set to the previously set maximum allowed vehicle speed plus adesired acceleration times the sample time in step 1724. Step 1724represents where maximum allowed vehicle speed is gradually rampedtoward zero.

When the answer to step 1710 is no, the brake engagement duration andthe first brake engagement duration are both set to zero and the desiredmaximum vehicle speed is set to the current vehicle speed in step 1720.When the answer to step 1714 is no, the maximum desired vehicle speed isset to the current vehicle speed and the brake engagement duration isincremented by sample time in step 1722.

In this way, the desired vehicle trajectory is determined based on thecurrent vehicle speed and the position of the gear selector (PRNDL).Further, the desired vehicle trajectory is adjusted based on actuationor engagement of the brake pedal. In particular, the length ofengagement of the brake pedal is used to adjust the desired vehicletrajectory. For example, the desired vehicle speed trajectory isdecreased while the brake pedal is engaged and set to the value of theactual vehicle speed when the brake pedal is released in some cases. Inthis way, improved drive performance can be achieved since allparameters indicative of the driver's desired vehicle operation arebeing incorporated.

Referring now to FIG. 17B, an example of operation is described whilethe accelerator pedal is released (i.e., closed pedal operation). Thetop graph shows the brake actuation signal and the bottom graph showsthe maximum allowed vehicle speed trajectory. At time t1, the brake isdepressed and released at time t2. While the brake is pressed themaximum allowed vehicle speed is set to the current vehicle speed, andthus no control action is taken. Since time difference Δt1 is less thanthe predetermined brake duration, the ramping of the maximum allowedvehicle speed is then continued until the brake is depressed again attime t3. The brake is then released at time t4. Since time differenceΔt1 is greater than the predetermined brake duration, the vehicle speedupon release at time t4 is captured and held as the maximum allowedvehicle speed.

Referring now to FIG. 18, a routine is described for determining, insome cases, whether the torque converter should be locked. Inparticular, the routine determines whether the torque converter can belocked during a closed pedal operation. First, in step 1810, adetermination is made as to whether the state machine is in case 3 andwhether the torque converter is presently unlocked. When the answer tostep 1810 is yes, the torque converter can be locked in step 1820. Inother words, the torque converter can be locked when the engine torqueis less than a small, predetermined negative torque value. In otherwords, the torque converter can be locked after the vehicle hastransitioned through the zero torque point. This is especiallyadvantageous if it is desired to unlock the torque converter when thedriver again depresses the accelerator pedal and requests positivepowertrain output. In particular, under this situation, the torqueconverter can be unlocked and thus provide a rapid amount of powertrainoutput, thus improving vehicle performance feel.

Referring now to FIG. 19, a graph illustrating typical operationaccording to the present invention is shown. The graph plots enginebrake torque versus time for a tip-out. The dash line illustrates thedesired engine torque value determined from, for example, the driveractuated element. The solid line indicates the actual engine torqueproduced. At time T1, the driver releases the foot pedal and the tip-outsituation is begun. The algorithms, according to the present inventionas described herein, first reduce the engine torque by a predeterminedamount. Then, the engine torque is gradually decreased at apredetermined rate, which is determined by a selected tip-out torquedecrease trajectory. The engine torque is decreased until it reaches asmall positive value (TQE₁₃ SML₁₃ POS). Maintaining the torque converterinput speed greater than the torque converter output speed holds thissmall positive torque. Then, at time T2, there is a decision to providenegative engine torque based on the vehicle trajectory. In particular,at time T2, the actual vehicle speed becomes greater than the maximumallowed vehicle speed plus a predetermined calibratable value. Startingat time T2, the engine torque is gradually decreased at a predeterminedrate through the zero torque point. Also, in this region, torque linecan be used using the torque converter input and output speeds to learnthe zero torque point and to update the engine torque model. Then, attime T3, a small negative torque is held by maintaining the torqueconverter output speed greater than the torque converter input speed.This small negative torque is held for a short period until, at time T4,a decision is made to lock the torque converter to provide high levelsof negative torque. At time T4, the torque converter is locked. Then,the negative torque level is selected to maintain the desired vehiclespeed trajectory. The negative torque level is selected such that theactual vehicle speed is generally below the maximum allowed vehiclespeed.

Referring now to FIGS. 20 and 21, two circuit torque converter 11 a isshown. FIG. 20 shows the two circuit torque converter clutch disengaged,while FIG. 21 shows the two circuit torque converter clutch engaged. Twocircuit torque converter 11 a is shows having input shaft 13 a, which iscoupled to engine crankshaft 13, and output shaft 17 a, which is coupledto transmission input shaft 17. Two circuit torque converter 11 a hasconverter clutch 200 a. Two circuit torque converter 11 a is disengagedby supplying pressure to the clutch control side of the clutch. Thepressure is exhausted through the impeller side of the converter. Theexhaust fluid is sent to a cooler. In particular, the clutch controlpressure must work against the pumping action of the impeller. To applythe converter clutch, fluid flow is reversed.

Referring now to FIGS. 22 and 23, three circuit torque converter 11 b isshown. FIG. 22 shows the three circuit torque converter clutchdisengaged, while FIG. 23 shows the three circuit torque converterclutch engaged. Three circuit torque converter 11 b is shows havinginput shaft 13 b, which is coupled to engine crankshaft 13, and outputshaft 17 b, which is coupled to transmission input shaft 17. Two circuittorque converter 11 b has converter clutch 200 b. In FIG. 22, fluid issupplied to both the impeller side and to the converter clutch controlcircuit of the converter. This prevents the clutch from being engaged.The purpose of orifice 202 b on the converter inlet side is to reducethe amount of pressure on the converter side of the clutch. Thehydraulic pressure in the front chamber becomes greater than pressure inthe rear chamber, holding the converter clutch away from the convertercover and releasing lock-up. During lock-up mode, in FIG. 23, fluid isallowed to exhaust through the clutch control circuit, thereby allowingthe converter clutch piston to apply. Hydraulic pressure in theconverter side of the clutch causes the converter clutch to presstightly against the converter cover. Lock-up occurs and power istransmitted directly to transmission 15 with no fluid slippage.Converter in oil is fed directly, without an orifice. Converter outputis restricted by orifice 204 b to ensure the pressure builds up on theconverter side of the lock-up clutch.

The inventors of the present invention have found that torque converter11 a is more difficult to lock when transmitting large negative torque(impeller spinning much slower than turbine) than torque converter 11 b.A potential explanation of this is that when the impeller is spinningslower than the turbine, the turbine is pushing oil into the impeller,rather than the other way. It is then hard to build pressure on theturbine side to push the clutch on.

However, those skilled in the art will recognize, in view of thisdisclosure, that the method of the present invention is not limited totwo circuit torque converters. In particular, this aspect of the presentinvention is applicable to any torque converter that would be difficultto lock when transmitting large negative torque values. For example,this difficulty may be due to inability to build hydraulic pressure orinability to exhaust hydraulic pressure. Typically, this type of torqueconverter has insufficient hydraulic pressure to be locked whentransmitting a predetermined amount of negative torque. Thispredetermined amount of negative torque can be determined using torqueconverter input and output speeds. For example, when output speed isgreater than input speed by a predetermined amount, the torque converterhas insufficient hydraulic pressure to be locked.

Further, the inventors have recognized that it is possible to minimize“clunk” by providing an un-locked torque converter when passing throughthe zero torque point (or transmission lash zone). And, at the sametime, provide maximum availability of negative powertrain torque with alocked torque converter by locking the torque converter aftertransitioning through the lash zone.

What is claimed is:
 1. A method for controlling a powertrain of avehicle, the method comprising: detecting operation of a first driveractuated element; detecting operation of second driver actuated element,said second detected operation is duration of a brake actuator;detecting operation of a third driver actuated element; and determininga desired vehicle condition based on said detected first, second, andthird driver actuated elements.
 2. A method for controlling a powertrainof a vehicle, the method comprising: detecting operation of a firstdriver actuated element; detecting operation of a second driver actuatedelement; determining a parameter related to duration of operation ofsaid second driver actuated element; and determining a desired vehiclecondition based on said detected first driver actuated element and saidparameter.
 3. The method recited in claim 2 wherein said second elementis a brake actuator.
 4. The method recited in claim 2 wherein saiddesired vehicle condition is desired vehicle acceleration.
 5. The methodrecited in claim 2 wherein said desired vehicle condition is desiredpowertrain output torque.
 6. An article of manufacture comprising: acomputer storage medium having a computer program encoded therein forcontrolling a powertrain of a vehicle, said computer storage mediumcomprising: code for detecting operation of a first driver actuatedelement; code for detecting operation of a second driver actuatedelement; code for determining a parameter related to duration ofoperation of said second driver actuated element; code for detectingoperation of a third driver actuated element, wherein said third driveractuated element is position of a transmission lever; and code fordetermining a desired vehicle condition based on said detected firstdriver actuated element, said detected third driver actuated element,and said parameter.
 7. The article recited in claim 6 wherein said firstelement is pedal position.
 8. The article recited in claim 6 whereinsaid second element is a brake actuator.
 9. A method for controlling apowertrain of a vehicle, the method comprising: detecting operation of afirst driver actuated element; detecting operation of a second driveractuated element; detecting operation of a third driver actuatedelement; determining a desired vehicle acceleration based on saiddetected first, second, and third driver actuated element; calculatingan actual vehicle acceleration; and adjusting an output of thepowertrain so that said actual vehicle acceleration approaches saiddesired vehicle acceleration.
 10. The method recited in claim 9 whereinsaid first element is a drive pedal.
 11. The method recited in claim 9wherein said second element is a brake actuator.
 12. The method recitedin claim 9, wherein said third element is a gear selection lever. 13.The method recited in claim 9, wherein said second detected operation isduration of a brake actuator.